While we’re on the subject of Rawls, I might as well pose the obvious question that follows from the argument I presented: it’s all well and good to say Rawls’ thought experiment leads to the best understanding of how to create a fair society, but who says fair is so great in the first place?
This is similar to the challenge posed by Thrasymachus: who says your metrics for goodness are objectively good? This is the question that led me to metaethics, because I realized that I didn’t have a very good response. I couldn’t bring myself to argue that ethical claims were natural properties, but I was uncomfortable with moral relativism, for obvious reasons.
But before I get into some possible answers, I want to solicit your opinions: what are ethical claims rooted in? Anything? When you say “Murder is wrong,” are you actually expressing an objective fact?